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<div class="titlepage"><div><div><h5 class="title">
<a name="spirit.karma.reference.operator.plus"></a><a class="link" href="plus.html" title="Plus Generator (+a)">Plus Generator
          (<code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code>)</a>
</h5></div></div></div>
<h6>
<a name="spirit.karma.reference.operator.plus.h0"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.plus.description"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.description">Description</a>
          </h6>
<p>
            The Plus generator is used to repeat the execution of an embedded generator
            one or more times. It succeeds if the embedded generator has been successfully
            executed at least once.
          </p>
<h6>
<a name="spirit.karma.reference.operator.plus.h1"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.plus.header"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.header">Header</a>
          </h6>
<pre class="programlisting"><span class="comment">// forwards to &lt;boost/spirit/home/karma/operator/plus.hpp&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">karma_plus</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
            Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
          </p>
<h6>
<a name="spirit.karma.reference.operator.plus.h2"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.plus.model_of"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.model_of">Model
            of</a>
          </h6>
<div class="blockquote"><blockquote class="blockquote"><p>
              <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a>
            </p></blockquote></div>
<h6>
<a name="spirit.karma.reference.operator.plus.h3"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.plus.expression_semantics"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.expression_semantics">Expression
            Semantics</a>
          </h6>
<p>
            Semantics of an expression is defined only where it differs from, or
            is not defined in <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a>.
          </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Semantics
                    </p>
                  </th>
</tr></thead>
<tbody><tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The generator <code class="computeroutput"><span class="identifier">a</span></code>
                      is executed one or more times depending on the availability
                      of an attribute. The execution of <code class="computeroutput"><span class="identifier">a</span></code>
                      stops after the attribute values passed to the plus generator
                      are exhausted. The plus generator succeeds as long as its embedded
                      generator has been successfully executed at least once (unless
                      the underlying output stream reports an error).
                    </p>
                  </td>
</tr></tbody>
</table></div>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
              All failing iterations of the embedded generator will consume one element
              from the supplied attribute. The overall <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code> will succeed as long as at least
              one invocation of the embedded generator will succeed (unless the underlying
              output stream reports an error).
            </p></td></tr>
</table></div>
<h6>
<a name="spirit.karma.reference.operator.plus.h4"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.plus.attributes"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.attributes">Attributes</a>
          </h6>
<p>
            See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.karma.quick_reference.compound_attribute_rules.notation">Compound
            Attribute Notation</a>.
          </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Attribute
                    </p>
                  </th>
</tr></thead>
<tbody><tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code>
                      (unary <code class="computeroutput"><span class="special">+</span></code>)
                    </p>
                  </td>
<td>
                    <p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="special">+</span><span class="identifier">a</span><span class="special">:</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="special">+</span><span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span></pre>
<p>
                    </p>
                  </td>
</tr></tbody>
</table></div>
<div class="important"><table border="0" summary="Important">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../images/important.png"></td>
<th align="left">Important</th>
</tr>
<tr><td align="left" valign="top"><p>
              The table above uses <code class="computeroutput"><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span></code> as a placeholder only. The notation
              of <code class="computeroutput"><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span></code>
              stands for <span class="emphasis"><em>any STL container</em></span> holding elements
              of type <code class="computeroutput"><span class="identifier">A</span></code>.
            </p></td></tr>
</table></div>
<p>
            The Plus generator will execute its embedded generator once for each
            element in the provided container attribute as long as the embedded generator
            succeeds. On each iteration it will pass the next consecutive element
            from the container attribute to the embedded generator. Therefore the
            number of iterations will not be larger than the number of elements in
            the container passed as its attribute. An empty container will make the
            plus generator fail.
          </p>
<p>
            It is important to note, that the plus generator does not perform any
            buffering of the output generated by its embedded elements. That means
            that any failing element generator might have already generated some
            output, which is <span class="emphasis"><em>not</em></span> rolled back.
          </p>
<div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top">
<p>
              The simplest way to force a plus generator to behave as if it did buffering
              is to wrap it into a buffering directive (see <a class="link" href="../directive/buffer.html" title="Generator Directive for Temporary Output Buffering (buffer[])"><code class="computeroutput"><span class="identifier">buffer</span></code></a>):
            </p>
<p>
</p>
<pre class="programlisting"><span class="identifier">buffer</span><span class="special">[+</span><span class="identifier">a</span><span class="special">]</span></pre>
<p>
            </p>
<p>
              which will <span class="emphasis"><em>not</em></span> generate any output in case of
              a failing generator <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code>. The expression:
            </p>
<p>
</p>
<pre class="programlisting"><span class="special">+(</span><span class="identifier">buffer</span><span class="special">[</span><span class="identifier">a</span><span class="special">])</span></pre>
<p>
            </p>
<p>
              will not generate any partial output from a generator <code class="computeroutput"><span class="identifier">a</span></code> if it fails generating in the middle
              of its output. The overall expression will still generate the output
              as produced by all successful invocations of the generator <code class="computeroutput"><span class="identifier">a</span></code>.
            </p>
</td></tr>
</table></div>
<h6>
<a name="spirit.karma.reference.operator.plus.h5"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.plus.complexity"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.complexity">Complexity</a>
          </h6>
<div class="blockquote"><blockquote class="blockquote"><p>
              The overall complexity of the plus generator is defined by the complexity
              of its embedded generator multiplied by the number of executed iterations.
              The complexity of the plus generator itself is O(N), where N is the
              number of elements in the container passed as its attribute.
            </p></blockquote></div>
<h6>
<a name="spirit.karma.reference.operator.plus.h6"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.plus.example"></a></span><a class="link" href="plus.html#spirit.karma.reference.operator.plus.example">Example</a>
          </h6>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
              The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.karma.reference.basics.examples">Basics Examples</a>
              section.
            </p></td></tr>
</table></div>
<p>
            Some includes:
          </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">karma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">support_utree</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">phoenix</span><span class="special">/</span><span class="identifier">core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">phoenix</span><span class="special">/</span><span class="keyword">operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">std_pair</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">proto</span><span class="special">/</span><span class="identifier">deep_copy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">string</span><span class="special">&gt;</span>
</pre>
<p>
          </p>
<p>
            Some using declarations:
          </p>
<p>
</p>
<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">double_</span><span class="special">;</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">space</span><span class="special">;</span>
</pre>
<p>
          </p>
<p>
            Basic usage of a plus generator:
          </p>
<p>
</p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">v1</span><span class="special">;</span>
<span class="identifier">v1</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">1.0</span><span class="special">);</span>
<span class="identifier">v1</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">2.0</span><span class="special">);</span>
<span class="identifier">v1</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">3.0</span><span class="special">);</span>
<span class="identifier">test_generator_attr_delim</span><span class="special">(</span><span class="string">"1.0 2.0 3.0 "</span><span class="special">,</span> <span class="special">+</span><span class="identifier">double_</span><span class="special">,</span> <span class="identifier">space</span><span class="special">,</span> <span class="identifier">v1</span><span class="special">);</span>
</pre>
<p>
          </p>
<p>
            A more sophisticated use case showing how to leverage the fact that plus
            is failing for empty containers passed as its attribute:
          </p>
<p>
</p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">v2</span><span class="special">;</span>               <span class="comment">// empty container</span>
<span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"empty"</span><span class="special">,</span> <span class="special">+</span><span class="identifier">double_</span> <span class="special">|</span> <span class="string">"empty"</span><span class="special">,</span> <span class="identifier">v2</span><span class="special">);</span>
</pre>
<p>
          </p>
</div>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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